Brake bleeding help

So I'm trying to bleed/flush my brakes. They bleed fine from the calipers, and I get fluid from all 4. I'm starting from the passenger rear, then driver rear, then passenger front, and finally driver front.

When I bleed with the truck off, the pressure builds on the pedal, until I get a firm pedal. Once I'm done bleeding all 4 wheels, I turn the engine on, and then the pressure in the brake pedal seems to get lost, and it just goes to the floor.

Not sure what to do at this point.

I'm thinking maybe something is going on with the master cylinder, maybe air got all the way up there.

Any help would be appreciated.

 

Stupid question, but are you refilling the brake reservoir in between each brake the you bleed?

 

Maybe bleed it running?
Are you doing gravity or a two person pump the pedal?

 

Not between each brake, but I am checking the reservoir, and making sure it never gets below the "min" line on it

 

Two person procedure. I'm having him pump the pedal 3 times, then hold it down, while I open the valve, let it run for a few seconds, then close the valve, and have him release the pedal.

 

I haven't tried bleeding it with the engine running, because most of the instructions on it say to do it with the engine off.

 

Are you doing it by yourself or with another person?
The order you have is correct.
Passenger rear: crack the bleeder, press and hold brake, close the bleeder, release brake. Do this until all air bubbles are out. Fill master cylinder to max line.
Repeat process for driverside rear.
Repeat process for passenger front.
Repeat process for driverside front.

 

Engine off.....not on. You have the sport, not the offroad.

 

Yes I have a sport. But it's weird that it loses pedal firmness once the engine is turned on.

That's what's making me wonder if there's a problem in the master cylinder or with the vacuum pump or something along those lines.

 

Turn in on and repeat your bleeding procedure. I always bleed my sport running with 1 person pumping and holding. Never a prob. With no power you will loose pressure just like what’s happening.

 

Is there any chance that bleeding it while it with the engine is running would cause any problems or damage?

 

you are about right, I just dont count the pedal pushes. I have the person inside pump the brakes till its hard to push the pedal, have the person press one final time at the same time open the bleeder, then let it run a split second (should be a steady stream no bubbles) then close it off. repeat for each. Dont do it with the truck running.

 

You can do it with the engine off but with the key in the on position. Have you been doing this?

 

Yes, that's how I've been doing it. Key in the On/ACC position, but engine off.

 

Another stupid question.....but you are using brand new brake fluid correct?

 

Yes

 

If it helps, I'm getting much more fluid from the front brake than I am from the rears.

 

Then you might want to get it checked out, you may have some small foreign object stuck in the lines or maybe a master cylinder problem.....but both of these are somewhat unlikely.....

 

I wouldn't discount the possibility of issues with the master cylinder, especially if air got up there. My truck has been sitting in the driveway with the lines open for about a week.

 

I bleed it running when I installed brake lines. Also did it on brake jobs and to flush the fluid